Skin tissue injury with latent carcinogenic potential after beta irradiation in mice

Murine skin cells were labelled with [3H]-TdR immediately after 90Sr-90Y beta irradiation with 30 Gy, and animals killed at different time intervals. The number of labelled cells decreased exponentially with time, and no labelled cells were found after 20 days. No unscheduled DNA synthesis was present at the lethal dose range, except at a dose of 300 Gy. When beta irradiation was repeated with a dose of 4.7 or 11.8 Gy 3 times a week, 100% skin tumour incidence was obtained within 550 days. 1.35 Gy per exposure caused neither depilation nor tumour induction during 300 days, when tumour incidence was 23% after 4.7 Gy. With 27 Gy per exposure once a week, no tumour was induced in 300 days. The authors conclude that repetition of irradiation is necessary to obtain a high tumour incidence and that an optimum dose range per exposure exists of between 5 and 10 Gy. (UK)